Transmission of NPV in uniform- and mixed-age populations ofHeliothis zea [Lep: Noctuidae] on caged soybean

Transmission of a nuclear polyhedrosis virus (NPV) was examined in uniformaged and uniform- vs mixed-age populations ofHeliothis zea (Boddie) on caged soybean. Larval collections revealed viral disease outbreaks occurred in all treatments following release of infected larvae (Primary infected larvae). Transmission of NPV in uniform-aged populations was related to the density of primary infected larvae released in the population but not to the size at death of primary infected larvae (P<0.05). In mixed-age populations horizontal transmission in the oldest larvae in the population was equal to that in uniform-aged populations, providing that primary infected larvae in the mixed-aged population were all the age of the oldest noninfected cohorts. As the mixed-age population aged, transmission increased and was generally higher than that in the uniform-aged populations. Transmission was also higher when primary infected larvae were medium sized at death than when small or large at death. The concentration of virus deposited on foliage and in soil after all larvae had died on plants was related to density of primary infected larvae released. In soil, but not on foliage, the virus concentration was related to the size at death of primary infected larvae released. This material is based upon work supported in part by the U.S. Department of Agriculture under Agreement No. CRSR-2-1000.